I hope this is useful for someone. It may be I'm just using the wrong kind of eraser, or maybe no one else even uses pencils, or maybe everyone already knows this trick. But, it was new to me, so I thought I'd share.
I sometimes draw or trace things with pencils and cut them out, and I sometimes measure and use pencil markings to help me line up stuff on my pages.
But when I have pencil marks that need to be erased, my eraser starts getting grey and dirty, and pretty soon instead of erasing it's just making smudges everywhere. Or it picks up stray smudges of glue and starts making a big mess.
So, to clean my eraser off, I discovered this simple trick: I just rub it on sandpaper and ta-da, good as new!
I hope this is helpful for someone, happy scrapping!